Regarding fixing it too, you could replace the BMS or whatever term you’re used to using for the balance circuitry for the battery but would suggest checking out this thread:
You’d want to check out each of the cells if possible (via balance lead connections or otherwise with a voltmeter) to make sure things are good. For the most part the biggest risk working with 18650s is shorting something especially once your series connections are made since it is a relatively high voltage thing then and with low resistance shorting across the +/- can deliver a lot of amps and become an unintentional spot welder.